1. Field of the Invention
The present invention relates to a method for the preparation of a condensate of a conjugated fatty acid, which permits the concentration of any conjugated fatty acid incapable of being purified according to the currently used fractional crystallization technique.
2. Description of the Related Art
The conjugated linoleic acid (CLA) has recently been attracted special interest since it possesses wide variety of physiological effects such as an effect of improving the metabolism of lipids, an effect of reducing the body fat, anti-cancer effect, an anti-allergic effect, and an anti-arteriosclerotic effect. The term “conjugated linoleic acid” means the generic name of fatty acids each having a conjugated double bond in the molecule and having 18 carbon atoms and a kind of fatty acid contained in meat and dairy products. It has in general been known that the conjugated linoleic acid can be prepared according to the alkali-conjugation technique (see Japanese Patent No. 3,017,108) while making use of an organic solvent represented by propylene glycol. The conjugated linoleic acid prepared according to this production method is an equimolar mixture comprising 9c, 11t-conjugated linoleic acid (9-cis, 11-trans-conjugated linoleic acid) and 10t, 12c-conjugated linoleic acid (10-trans, 12-cis-conjugated linoleic acid). In this respect, it has been known that these two isomers differ from one another in their physiological activities and side-effects and there has also been desired for the development of a condensate thereof which is enriched with a desired isomer.
On the other hand, as methods for the purification of fatty acids, there have been known, for instance, the fractional crystallization technique, the distillation technique, the urea adduct technique, the silver complex-forming technique, the enzymatic technique (using, for instance, a lipase). However, the distillation technique is not useful because a conjugated fatty acid has generally a high boiling point and is not heat-stable. In addition, the urea adduct method is likewise quite useful for the purification of fatty acids, but it is not suitable when the fatty acids purified by this method are used in food products and the practice thereof also requires great expense. Moreover, the silver complex-forming technique is also a method quite useful for the purification of unsaturated fatty acids, but it is not suitable when the fatty acids purified by this method are used in food products and the practice thereof also requires great expense. Furthermore, the enzymatic method requires a high production cost and it also requires the use of complicated operations. Finally, the fractional crystallization technique is a quite excellent method for the purification of fatty acids and, in general, it has widely been used, but it would be difficult to purify fatty acids having solidifying points very close to one another such as isomers of a conjugated fatty acid.
Up to now, there have likewise variously been investigated many methods for concentrating a specific conjugated linoleic acid to thus give a condensate thereof. For instance, there has been reported a method for isolating isomers which comprises the steps of reacting a conjugated linoleic acid with, for instance, methanol under acidic conditions to form a methyl ester derivative thereof and then precipitating the same in the form of crystals (see, for instance, Non-patent Article 1 specified below). However, this method requires the use of a step for derivatization of the conjugated linoleic acid and this would result in an increase of the production cost thereof and further the resulting product must be hydrolyzed after the separation of the reaction product in this method. In case where the desired conjugated linoleic acid is concentrated through the crystallization of the reaction product, but it is difficult to obtain any concentrate thereof having a sufficiently high content of a target substance. Further, there has also been known a concentrating method through chromatography, but this method requires great expense because of the use of a solvent and a column.
There has likewise been reported a method for purifying isomers of a conjugated linoleic acid, which comprises the step of subjecting a fatty acid mixture comprising isomers of a conjugated linoleic acid or glyceride esters of the isomers to a selective reaction carried out in the presence of a lipase and in a reaction system free of any organic solvent (see, for instance, Patent Article 1 specified below). Another method has been reported, which comprises the steps of reacting a mixture containing isomers of a conjugated linoleic acid with octanol in the presence of a lipase to thus change the compositional ratio of the isomers of the conjugated linoleic acid present in the octanol ester fraction (see, for instance, Patent Article 2 specified below). Moreover, a method has likewise been reported, which comprises subjecting isomers of a conjugated linoleic acid to a selective esterification reaction with a linear higher alcohol in the presence of a lipase to thus give a 9c, 11t-conjugated linoleic acid-containing fatty acid (see, for instance, Patent Article 3 specified below).
However, these methods make use of quite expensive lipases and they require the use of an additional operation (such as distillation step) for separating reaction products from un-reacted starting substances since they are ones in which any desired product is isolated based on the difference in the reactivity between each isomer of an unsaturated fatty acid with an alcohol or the difference in the susceptibility, to hydrolysis, of the derivatized isomers of an unsaturated fatty acid, observed in the presence of such lipases. In addition, regarding the derivatives of isomers, these methods further require the use of an extra operation such as an additional hydrolysis of such derivatives even after the isolation thereof. This may further increase the production cost. Moreover, the resulting product would not be favorable as an ingredient for foods depending on the kinds of alcohols used (for instance, in case wherein octanol is used as such an alcohol).
Patent Article 1: Japanese Un-Examined Patent Publication 2004-023810;
Patent Article 2: Tokuhyo Hei 11-514887;
Patent Article 3: Japanese Un-Examined Patent Publication 2001-169794; and
Non-Patent Article 1: O. Berdeaus, J. Voinot, E. Angioni, P. Jurneda and J. L. Sebedio, J. Am. Oil. Chem. Soc., 1998, 75:1749-1755.